June 22, 2012 AT 4:46 pm

Tutorial: Bi-Color 8×8 Matrix – Adafruit LED Backpacks

This version of the LED backpack is designed for these bright and colorful square=pixeled 8×8 matrices. They have 64 red and 64 green LEDs inside, for a total of 128 LEDs controlled as a 8×16 matrix. This backpack solves the annoyance of using 24 pins or a bunch of chips by having an I2C constant-current matrix controller sit neatly on the back of the PCB. The controller chip takes care of everything, drawing all 128 LEDs in the background. All you have to do is write data to it using the 2-pin I2C interface. There are two address select pins so you can select one of 8 addresses to control up to 8 of these on a single 2-pin I2C bus (as well as whatever other I2C chips or sensors you like). The driver chip can ‘dim’ the entire display from 1/16 brightness up to full brightness in 1/16th steps. It cannot dim individual LEDs, only the entire display at once.

Adafruit Bicolor LED Square Pixel Matrix with I2C Backpack – What’s better than a single LED? Lots of LEDs! A fun way to make a small colorful display is to use a 1.2″ Bi-color 8×8 LED Matrix . Matrices like these are ‘multiplexed’ – so to control all the 128 LEDs you need 24 pins. That’s a lot of pins, and there are driver chips like the MAX7219 that can help control a matrix for you but there’s a lot of wiring to set up and they take up a ton of space. Here at Adafruit we feel your pain! After all, wouldn’t it be awesome if you could control a matrix without tons of wiring? That’s where these adorable LED matrix backpacks come in. We have them in three flavors – a mini 8×8, 1.2″ Bi-color 8×8 and a 4-digit 0.56″ 7-segment. They work perfectly with the matrices we stock in the Adafruit shop and make adding a bright little display trivial.

The matrices use a driver chip that does all the heavy lifting for you: They have a built in clock so they multiplex the display. They use constant-current drivers for ultra-bright, consistent color, 1/16 step display dimming, all via a simple I2C interface. The backpacks come with address-selection jumpers so you can connect up to four mini 8×8’s or eight 7-segments/bicolor (or a combination, such as four mini 8×8’s and two 7-segments and two bicolor, etc) on a single I2C bus.